On the Performance of LoRa Chirp Modulation in the Presence of LR-FHSS Interference

In this paper, we investigate the coexistence between two of the most common long-range wide area network (LoRaWAN) transmission schemes, i.e., LoRa chirp and long-range frequency hopping spread spectrum (LR-FHSS). We consider a system model in which LoRa chirp and LR-FHSS modulations are deployed in two overlapping terrestrial and direct-to-satellite internet of things (DtS-IoT) networks, respectively. We derive the maximum likelihood (ML) detection rule for the joint detection of the LoRa chirp and the interfering portion of LR-FHSS fragments at the terrestrial LoRa gateway (GW). Due to the high complexity of the joint ML detector, and since our focus is primarily on the detection of the LoRa chirp at the LoRa GW, we propose a filtering-based detector for the LoRa chirp which benefits from the narrowband frequency characteristics of the LR-FHSS signal as the interference. Simulation results show that the error performance of the proposed filtering-based detection for the LoRa chirp degrades by 2 dB, 1 dB, and less than 0.5 dB for SF = 7, SF = 9, and SF = 11, respectively, at bit error rate (BER) of 10⁻⁴ in additive white Gaussian noise (AWGN), compared to the case when the LR-FHSS interference does not exist. Moreover, for Rayleigh fading channel conditions, the proposed filtering-based detection scheme can achieve an acceptable performance in high values of signal-to-interference ratio (SIR).